baxi 105e instant no hot water when heating running

[sfnett]

hello, i have a baxi 105e instant, the dhw works perfect as long as ch is not on. when the ch is running and you run dhw no problem until you stop running dhw then red 50 neon flashes and and dwh will not come back on until i turn the boiler off and let cool down abit . your advice would be greatly recieved thanks.
p.s i did change the dhw diaphram last year befor this problem started, and am now wondering if its the other diaphram in the diverter that needs doing?

 

[sfnett]

some more develepments the heating hasnt been on for a couple of days , had a shower last night and the water wasnt very hot just luke warm went down to the boiler ran a hot tap and the 50 neon was flashing stopped tap and boiler retuned to normal and hasnt happenned again since ? anyone any ideas please